How to check if window switches OK?

TomO · #1 06-24-2004, 05:39 PM

My right rear window goes down but not up. For a while it was intermittent, and would eventually go up if we jiggled the door or console switch enough. Now it is dead. I pulled the switch and checked continuity with an digi multimeter. I get continuity connecting pin 1&4 for the window down, and pins 1&3 for the window up. I can't get any continuity between pin 2 and any other pins (what is pin 2 for ?). I tried both rear window switches and both work the same. Also, the colors of wires are different on my car than the Haynes manual. Should they be? TIA!

d2bernhard · #2 06-25-2004, 04:14 PM

Check it on the other door. I would guess the wires in your door and b pillar have gone south.

TimP · #3 06-25-2004, 09:44 PM

I had a 280e with intermittent windows, and all the switches tested fine with the few mA of current from the meter. However the contacts were dirty enough that they had a large voltage drop across them with the relatively high current of the window motors.

I cleaned the switch contacts (this was a '77 and they were easily disassembled) with a product called Cramolin which is now called "De-Oxit" and it fixed all but one switch. I replaced that switch with a new one and it was fine.

Tim

Gilly · #4 06-25-2004, 09:50 PM

I'd agree with the suspicion of bad wires in the area of the door hinge (on the affected door), real common, the wires get brittle and crack/break. If you don't mind removing the door panel you can monitor the voltage at the window motor junction itself, while opening and closing the door, or remove the panel and gently tug on the wires where they enter the door.

Gilly

TomO · #5 06-27-2004, 09:22 PM

I've had the door panel off before so hopefully it will be easy to remove again (this time I took detailed notes on where to put my little prybars and screwdrivers to remove the outer plastic trim that holds the switches from the door).

As to the switches, I don't understand how they work, but does the fact that the window will not go up using either the door or the console switch in any way eliminate the switches as the problem?

Thanks

Gilly · #6 06-28-2004, 05:01 AM

No, it doesn't. A failed front switch can make the rear switch cease operating, so you have to be careful with your diagnosis. The small lockout switch on the console I don't think will "kill" both switches, not sure on that. I've also never seen a rear switch make the front switch fail to work that I remember.
If you can take the rear witch out and identify the 2 wires for the motor, you can jump power and ground to see if the motor is capable of operating, this is the first important test in knowing where your problem might be.

Gilly

TomO · #7 06-29-2004, 05:10 PM

I swapped the rear window switches with each other and then swapped the console rear switches with each other with no change in behavior of either rear window motors (i.e., right rear still fine, left rear still goes down but won't go up.) I also removed the left rear door panel and tried to gently tug on the wires while holding the switch for up, but nothing happens.

When I push the up switch I can hear the relay clicking under the rear seat. My hypothesis is that the window motor system thinks the window is already all the way up and won't give the motor any juice. Is there a cut-off switch on the motor that might be bad?

I hate to tear up the flooring of the car looking for a broken wire. It seems to me that it would be a lot easier to check for continuity of wiring using an ohmmeter, but as I mentioned earlier, my wire colors don't match the Haynes schematics and I wonder if MB changed the window system in 1994 (my Hanynes manual is for 1985 to August 93). Plus I don't fully understand how the Haynes diagram would work, especially the switches. Anyway, here are my 1994 E320 left rear switch colors: Pin1-Brown; Pin2 Grey/blue; Pin3 Blue/white; Pin4 Green/red. Haynes is Pin1 green; pin2 Black; pin3 green/red; pin4 brown; pin7 blue/white; pin 58 (the diode?) green/blue.

Any help will be greatly appreciated. My next move is to simply disconnect the left rear window motor wires (you can hardly drive the car with the windows down anyway).

hieber · #8 06-29-2004, 05:52 PM

Can a bad switch make a fuse blow on the power windows?

One circuit (front-driver/rear-passenger) works fine.

The other circuit (front-passenger/rear-driver) blows the fuse repeatedly. For example, put the window down, the fuse blows, and you can't put it up. Put in a new fuse and it blows.

The only way I can put the window back up is to; First, put in a new fuse, and secondly put the driver side switch into the passenger side receptacle.

Both switches have the same part number - but for some reason the switch in the passenger side pops the fuse.

Any ideas?

Thanks.

TomO · #9 06-29-2004, 06:02 PM

I forgot to mention that I can get my window up fine by disconnecting the motor wires in the door and applying 12v to the green and black leads. Also, to check the wires into the door pillar must I cut away all the black netting?

Heiber--you should probably repost your question as a new topic.

d2bernhard · #10 06-29-2004, 06:59 PM

Per TSB REF.NO. MBNA 54/19, 72/9 from 1988, the wires should be replaced from the B pillar to the window switch -- with new connector soldered in and re-routed into the wiring harnesses. Cut the wires in the B Pillar and connect new wires all the way through the door joint to the switch wiring harness. There used to be a kit with an MB part number, but is no longer available. Wiring harness of repair kit 124 540 27 35.

I got this from AllDataDIY.com -- sorry I cannot cut and paste the entire thing for you -- it is copywright protected. But is only costs $25 per year and $15 to add another or to renew.

This was to have been modified and fixed on the W124 in November 1987, but that's not to say it couldn't still happen.

Make sure you disconnect the battery! I toasted the illumination on my center console switch becaue I did not. Had to replace the entire switch.

Gilly · #11 06-29-2004, 09:40 PM

Heiber: I'd say it's safe to assume that this switch is bad, yes. As another test you could try plugging in the suspected "bad" switch into the opposing circuit (the one that doesn't blow a fuse) and see if the other fuse blows.....

Tom
You wouldn't have to cut anything, just disconnect the rubber bellows and slide the "tube" inside the door.

Gilly

TomO · #12 07-01-2004, 11:29 AM

I did some circuit testing and would appreciate help with my diagnosis. (Thanks to Jim who sent me links to benzworld where I found the correct wiring diagram (on a Russian website)--and it turns out I had printed the wiring diagram from the CD ROM last year but couldn't understand it then and forgot about it--duh). Indeed, the window wiring for the 94 E320 is totally different from older cars. I hooked up a voltmeter to the green/viol and black/viol wires that go into the door from the so-called "convenience control unit" located under the rear seat. These two wires are connected to the motor's green and black wires at a plastic block on the door. The way I figure it, the convenience control contains relays which reverse polarity of voltage to the motor depending on signals from the window switches. (And I had already determined that all my switches are OK by swapping them).

For my test I disconnected the motor wires and attached a multimeter to the green/viol and black/viol wires. When I hit the window switch I get 12.4 V, pos or neg, depending on whether up or down. Conclusion: the relay is getting the message to power window up and is trying to tell motor to go up. Then I connected light bulbs of various wattages to test the circuit under load. I started with an old H1 or H4 headlamp (about 0.5 ohm) and got full illumination and 12.0 V down but no illumination and 0.05V up. Conclusion: somehow the relay or the following circuit can't deliver the amps.

Then I tried the 5W (3 ohm) bulb out of the door ashtray and got a bright light and 12.34 V with the swich held down. With the window switch held in the up position the voltage started at 0.3 V and gradually increased to 1.1 V, while the bulb glowed very dim at first and gradually became less dim.

Then I hooked 4 tiny dash lights in series (23 ohms total) and got 12.37 V with switch down. With the switch up voltage gradually increased from 4.5 to 6 volts as the bulbs slowly got brighter. THEN, if I held the switch up for about 30 seconds the bulbs suddenly became much brighter and the voltage jumped to 12 V.

So I'm still guessing I have either a bad relay or a bad solder connection in the convenince control unit. I need help with the diagnosis at this point.

I read that the control unit is very expensive and it doesn't look very accessible. If so, I'm thinking a kluge (crude fix) might be the answer. I could wire in a DPDT switch between the door and motor wires and put the switch in the door ashtray. Throwing the switch would let the down window switch raise the window. (My wife's only criticism is she uses the ashtrays for litter bags.)

Any comments?

MrCjames · #13 07-01-2004, 12:19 PM

Try this for Window diagnosis.

1) Operate suspect window
2) Monitor dome lamp while illuminated
3) If dome lamp dims (Problem is in the door)
4) If dome lamp does not dim (Suspect Mstr/Slv/Motor/or Wires)

If wiring at the pillar is suspect
1) Turn headlights on
2) Safety switch "off"
3) Monitor switch lamp
4) Slowly open and close door
5) If lamp goes out (Suspect pillar wiring)
6) Operate window from suspect door while following Step 4
7) If window operates (Suspect Pillar wiring)

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